Apolipoprotein E (apoE) is a 299 amino acid protein present in VLDL, IDL and HDL that plays a major role in the metabolism of plasma lipoproteins. ApoE is a major ligand for the LDL and remnant receptors and thus, necessary for the normal clearance of remnant particles from the circulation. Patients with a functional deficiency of apoE can develop Type III hyperlipoproteinemia and premature atherosclerosis. Recently, apoE deficient mice have been generated by homologous recombination. These animals develop marked hypercholesterolemia and spontaneous vascular lessions and are a useful model for evaluating the potential for gene therapy. We have generated a recombinant adenoviral vector containing human apoE cDNA (rAdV) for injection of apoE def mice (n=8) with pre-tx lipids:TC=609plus/minus108mg/dl,TG=101plus/minus50mg/dl and chol-rich VLDL/IDL present on FPLC. After IV infusion of either ten to the seventh or ninth pfu, apoE-def mice had peak (day 6) plasma h-apoE levels of 2.3 mg/dl and 648 mg/dl, respectively. Western blot analysis demonstrated the expression of a normal sized h-apoE. Expression of these two different levels of apoE in plasma resulted in markedly different lipoprotein changes. Mice achieving physiologic apoE levels (2.3 mg/dl) normalized their lipids (TC=109plus/minus19mg/dl, TG=56plus/minus29mg/dl) at days 4-8; FPLC was normalized with loss of all VLDL/IDL and generation of HDL. Animals with 200X increase in apoE had a biphasic lipid response with initial decrease in TC (230mg/dl) but increase in TG (652 mg/dl); FPLC shifted from chol-rich VLDL/IDL to Tg-rich LDL remnants. By 8-12d apoE (less than 10mg/dl) and TG (66plus/minus40mg/dl) decreased and FPLC revealed a normal HDL profile. ApoE expression and normal plasma lipids were maintained for a period of 4 weeks after virus injection. Our studies indicate successful physiologic replacement (2.3mg/dl) as well as marked overexpression (more than500mg/dl) of h-apoE in apoE def mice using recombinant adenovirus as vehicle.Physiologic levels of h-apoE normalized plasma lipids whereas apoE overexpression resulted in transient formation of TG-rich remnants possibly due to high apoE levels blocking receptor mediated remnant clearance. Successful replacement of apoE in apoE-def mice demonstrates the feasibility of gene therapy in human apolipoprotein deficiencies.